I've been told that it's common for the last piston to wear first (ie: number 4 on a 4 banger).

Apparently because 4 is furthest from the radiator input it tends to be a bit warmer than the rest thereby promoting slightly abnormal wear.

Sounded like a good idea to me!

Screw in - needed to be for my old VR4.

I didn't do the oil thing yet, I was 1/2 thinking of rebuilding it anyway. I'll check the valve adjustment too.

is it a push-in or screw-in type gauge?

Anyway, squirt a little oil in #4 and test it again. If you get a higher reading it would tend to indicate rings.

Also check valve adjustment on #4 valves.

And before seriously contemplating a rebuild, a head off inspection would be a good idea. Could just be a burnt valve or poor valve seating...

190 to 175 psi..... never said my a12 was fast or good... maybe i cant read my guages for crap

My CA18DET before the rebuild, had 185psi on each of the back 2 cylinders and 120psi on the front Rings were on their way...


The service limit...

for A12 it's listed at 193psi, Minimum 179psi, but they say there shouldn't be a variance of more than 20%. More would indicate a mis-seating valve or broken ring. Uniform "Low compression" indicated worn rings.

The mechanic that owned the book before me had written in 181 and 142 as expected and min. All these values are at 350rpm.

This is according to the Nissan A10-A12 Factory Manual

Chris

the reading is enough to warrant attention, however, i always have or see problems with cyl 4 or 2, whats the deal with that?

Engine would be ok to run as is, but may not survive supercharging. maybe put new rings in it and bearings to freshen it up.
Im supprised your readings are that high too, im used to seeing about 140psi across all 4

I got 175psi across the board except for cly#4 which has 150psi, this is on an A14. What's the service limit on this? The difference is a worry, should I rebuild it or just suck it & see. Planning to supercharge it & at least rebuild/port the head and add a cam anyway.

Cheers
Ash